Automatic printing telegraph exchange system



Aug. 22, 1939. G. s. VERNAM 2,170,669

AUTOMATIC PRINTING TELEGRAPH EXCHANGE SYSTEM Filed Feb. 20, 1937 4Sheets-Sheet 1 LLLL TEN LINE RELAYS MULTIPLE T0 In N F IG. 1.

AC DC SUPPLY FIG. 3.

INVENTOR GILBERT 6'. VEfi/VAM ATTO R N EY Aug. 22, 1939.

OPERATORS pm/vrm FIG2.

G. S. VERNAM AUTOMATIC PRINTING TELEGRAPH EXCHANGE SYSTEM Filed Feb. 20,1937 FINDER com/zero? 33 snare/1 4 Shets-Sheet 2 INVENTOR I G/LBERTS.VER/VAM ATTO R N EY ACORDC J'UPPLY FIG. 4.

s. VERNAM 2,170,669

AUTOMATIC PRINTING TELEGRAPH EXCHANGE SY$TEM Filed Feb. 20, 1937 4Sheets-Shee t :5

F/NDEMS OTHER U/VE RELAYS LLLLL MULTIPLE TO OTHER GILBERT 5. VE/PNAMATTORNEY G. S. VERNAM AUTOMATIC PRINTING TELEGRAPH EXCHANGE SYSTEM 4Sheets-Sheet 4 Aug. 22, 1939. 2,170,669

Filed Feb. 20, 1937 ATTORNEY patented Aug. 22, 1939 AUTOMATIG'PRINTINGTELEGRAPH EX CHANGE SYSTEM Gilbert 5. Vernam, Hackensack, N. J assignorto I Postal Telegraph-Cable Company (New York),

New York, N. Y., a corporation of New York Application February 20,1937, Serial No. 126,769

16 Claims.

My invention relates in general to printing telegraph systems and moreparticularly to automatic printing telegraph exchanges and concentratorcircuits for interconnecting subscribers stations to the central officeoperators stations.

In automatic printing telegraph exchange systems .heretofore in use ofthe type employing single wire subscribers lines, special apparatus hasbeen necessary at the subscribers stations, due to the fact that, ingeneral, the automatic system works with a normal low line currentwhereas in the manual concentration systems the line current is normallymuch higher. One of the objects of my invention is to provide a linerelay circuit at the central office which permits operation with eithernormal high line current or normal low line current, thus permitting thesame type of subscribers' station apparatus to be used interchangeablywith either manual or automatic concentration systems, and alsopermitting the same type of central ofiice equipment to be usedinterchangeably with either the .standard high line'current subscribersapparatus or with the special low line current subscrib-ers apparatus.

It is a further object of my invention to reduce the number of automaticswitches otherwise required, by establishing direct semi-permanentconnections between certain subscribers lines and central oificeprinters during periods of heavy traffic. It is a further object of myinvention to apply the relay circuit to automatic concentrators orprinter exchanges of various sizes and also for operating callingsignals and controlling the motors of direct connected printers.

Accordingly one of the main ,features of my invention is the provisionof a line relay and a cut-off relay in each subscribers line at thecentral-office, so arranged that an inward call can be initiated eitherby increasing a normally low line current or by first decreasing andthen increasing a normally high line current. I

Another feature of my invention is the provision of separate printersets at the central oflice which may be plugged directly into asubscribers line, during periods of heavy traffic, without extending theconnection through the automatic switches usually employed inestablishing connections with subscribers stations. 7

Still another feature is the provision of relays associated with theseparate central ofiice printer sets for the purpose of operating acalling signal and automatically starting the printer motors of both thecentral ofiice and subscribers station printers when a call is made ineither direction.

Other features of my invention will be apparent from the followingdescription, as well as from the appended claims.

Thepreferred embodiment of my invention is illustrated in theaccompanying drawings, in which 1 Fig. 1 illustrates a high currentsubscribers station of the type usually used with manual concentratorsconnected to line and cut-off relays at' a central office adapted foruse as part of a hundred line automatic concentrator,

I Fig. 2 diagrammatically indicates the remainder "of the apparatusconstituting a hundred line automatic concentrator, including thecentral o'fii'ce operators printer,

- Fig 3 illustrates a subscribers station of the usual automatic ornormal low current type adapted to be connected with the same type ofline and cut-off relays at the central oifice,

Fig. 4 illustrates a circuit similar to that shown inFig. 1 but adaptedto a thousand line automatic concentrator or printer exchange system,

Fig. 5 illustrates diagrammatically further apparatus at the centraloffice for cooperation with the circuit of Fig. 4,

6 illustrates the normal low current subscribers station for connectionwith the thousand line concentrator or printer exchange system, and

' "Fig. 7 illustrates a circuit arrangement of the printer set fortabling busy lines.

In the drawings the same reference characters are generally used to showsimilar apparatus in the various figures.

Referring now'to Figs. 1 and 2, the numeral indicates generallya'subscribers station connected through a line 3 to the centralolficeline relay 'circuit'design'ated generally as 5. This circuit isassociated with the central office apparatus illustrated generally inFig. 2. The par- 40 ticular apparatus used in thecentral station may beof any desired type and as it does not form a part of this invention itaccordingly is shown in' Fig. 2 merely in block diagrams. A particularexample of such apparatus is shown in my Patent 1,910,867 issued May 23,1933.

A more particular description of the circuit shown in Figs. 1 and 2follows.

Normally a relatively high current, for example, about milliampers flowsfrom negative 50 battery 10 at the central oflice through the upperwinding" of cut-off relay II, jack 200, resistance R, back'contact B oiline relay 23, front contact A o-f-cut-off relay ll, line 3 through thewinding of polar relay ll, winding of motor control relay 39, armatureand front contact A of polar relay l1, through calling key 2! to groundat the subscribers station. This holds cut-oil relay II and polar relayll energized. Equalizing resistors R are provided in each subscribersline to enable adjustment to correct for differences in line resistance.To call from a subscribers station, the calling key is depressed andreleased, thus opening and closing the line. When the line is openedcut-ofi relay l I releases, and when the line closes line relay 23operate through back contact B of cut-off relay H. Polar-relay ll andcontrol relay 33 at the subscribers station release when the line isopened and are again reenergized upon closing of the line but this hasno effect except to start and momentarily run the motor 4| during theinterval while the line is open at calling key 2 I. The printer cannotbe operated, however, as its circuit is open while key 2| is depressedand it is short-circuited immediately through contact A of polar relayi! when key 2i is released. This short -circuit prevents the subscriberfrom sending during the intervalwhile motor l l is running, but slowingdown immediately after key2l is released. Without this short-circuit, itwould be possiblefor the subscriber to send signals from his printerkeyboard which would vibrate relay 39 and cause motor 4| to continue torun. Such signals would not be properly received at the central offioeas the central ofice printer is not yet connected to the line and mightresult in lost messages. With the cut-off relay il released and linerelay 23 operated, relay contacts 22 and 2 4 are closed and ground isapplied to the test bank terminals T of the finder connectors, and slowoperating group relay 25 operates toclose switch 21 grounding start lead29 of the idle position locator or allotter 3i, causing the first idlefinder connector 33 to find the calling line and to connect it tooperators set 35. When the finder connector cuts in on the calling line,ground is applied to the private bank terminal P energizing the lowerwindings of relays II and 23 inseries by battery 31. This operates tolock line relay 23 in its operated position and operates cut-01f relay Hwhich removes the ground previously applied to the testbank terminal'land relay 25 and extends the callingline through front contacts A ofrelays H were, and the line bank terminal L, which is now'conneoted tothe central office printer. Current from a positivebattery associatedwith the central ofiice printer set 35 causes the subscribers stationpolar relay IT to release, shorting out motorcontrol relay 39 throughback contact B, causing it to release, and starting printer motor 4!.This also permits the line current to traverse printer keyboard andmagnet 43 by removing the short circuit. Messages may now be transmittedbetween the subscribers station and the central ohice. Polar relay I!remains released, with its armature against back contact B during thetransmission ofprinter signals, as the armature is held against 3 by aspring (not shown) when the circuit is open and is held against the samecontact by current from the positive battery when the circuit is closed.

When the idle finder connector switch 33 and its associated printer set35 were first selected by the allotter 3!, the dial lead of set 35 wasmomentarily grounded by the allotter, thus operating relay 55, whichlocks itself'through release key 56. Ground from release key 56 overdial lead 58 serves to hold the finder connector switch to prevent itfrom releasing. After the message has been transmitted by the subscriberand acknowledged by the central office operator, the connection may bereleased from the central oifice in the usual way, the operatordepressing his release key 56 which releases relay 55 and removes theholding ground from the dial lead allowing finder connector switch 33 torelease. The release of the finder connector removes ground from theprivate bank terminal P. This releases line relay 23 immediately butcut-off relay H is made to be slow releasing and remains operated untilthe line relay 23 has released and closed the line circuit through theupper winding of cut-off relay ll, so that the control relay remains.operated and the circuit is restored to its normal idle condition.Current from negative battery l operates polar relay I I, removing theshort circuit from control relay 39 to stop the printer motor at thesubscribers station.

Turning now to Fig. 3 in connection with Figs. l and 2, theoperation ofthe system with subscribers stations arranged for normal low currentlines will be described.

With this system the line 3 norm-ally carries a very low current, forexample, about six milliamperes which is notstrong enough to operatecut-off relay H and therefore it is normally released. Likewise the lowcurrent is insufficient to operateline relay 23. The polar relay 51 atthe subscribers station (Fig. 3) is provided with two windings, winding53 of high resistance, and winding 55 oflow resistance. Operation ofcalling key 51 functions to short circuit high resistance winding 53 ofpolar relay and the line current from battery at the central station isincreased to a value sufiicient to operate line relay 23. This groundsthe test bank terminals and operates group relay 25 causing the line tobe switched through to the central office operators printer set in thesame manner as described in connection with Fig. 1. Current from thepositive battery at thecentral oificecauses the station polar relay .5!to release thus operating control relay 39 and starting printer motor4|. The calling key should now be restored to its normal position sincethe control relay contacts shown at 59 now shunt the high resistancewinding of polar relay 5|. Connection is ;now established between thesub scribers station and the operators station. The release circuit forthe system shown in Fig, 3 is in general substantially the same as thatin Fig. 1, however this difference occurs. After line relay 23 hasreleased, and the polar relay 5| at the subscribers station hasreleased, theline current reduces tothenormal low current value sincethe shunt is removed from winding 53 and thus allows cut-oi? relay i l Hto release restoring the circuit to its normalunoperated position. 7,

Qutwardcalls from the central oflice to the subscribers are handledsubstantially in the same manner as in the previously constructedcircuits, i. e. the eentral ofiice operator operates a dial to causethefinder connector associated with. her setto step its wipers to theterminals of the desired customers line, to test the line to determinewhether it is busy, and if not busy to connect with the bank terminal ofthe line. When the finder connector 33 grounds the private bank terminalP of the called line, the lower windings of line relay 23 and cut-ofirelay II are energized. .In the circuit as shown in Fig. 1 thecut-ofi.relay remains operated and the line thelow current line, both linerelays 23 and cut-01f relay II operate upon grounding of the privatebank terminal, resulting in a through line connection and the startingof the printer motor. In the low current station system, the line relay23 may operate slightly faster than the cut-01f relay II in which case ashort impulse of current will be sent through group relay 25. In orderto prevent such a short impulse applied to relay 25 from falselystarting the position selector on outward calls, relay 25 is made slowoperating, so that it will not respond to such short pulses.

The system shown in Figs. 4, 5 and 6, is applicable to a thousand lineautomatic concentrator or printer exchange system. This may be any typeof concentration system including systems in which separate groups ofoperators printers are used at the central station for inward andoutward calls such as illustrated in my prior Patent No. 1,895,113issued on January 24, 1933, and further may be connected to an exchangesystem which permits each subscriber to communicate through a tollboardwith other systems or through repeater control with other subscribers ina manner, for example, such as described in the patent to F. G. Hallden,No. 1,895,097, issued January 24, 1933. The system generally, as shownin these figures, is broadly the same as that shown in Figs. 1 and 2 soa detailed description only will now be given.

The private bank terminals of line finders in these thousand lineconcentrators are open when the corresponding line is idle, groundedwhen busy and connected to battery when the line is calling. Inanswering an incoming call the line finders hunt for battery on theprivate bank terminals instead of hunting for a ground on separate testbank terminals, as in the case of the hundred line combination finderconnector, described above. For this reason the line relay 23 is wiredso that, when operated, it connects the battery through its own windingand that of the cut-off relay II to the private bank terminals P. Exceptfor this change in wiring the relay circuit shown in Fig. 4 issubstantially the same as that shown in Fig. 1.

Since this concentration and exchange system may provide for selectiveservice as set forth in the above patents referred to, dial IOI has beenshown in connection with the subscriber's station, in Fig. 5. However,the system could be used without the dial if this selective service isnot required, in which case the subscribers station circuit of Fig. 1would be used in connection with the line and cut-0.1T relays of Fig. 4.

At the subscribers station, as shown in Fig.

4, a calling dial IOI is shown and a milliammeter I03 is provided in theline. Printer magnet coils 43 are normally short circuited by the makeor front contact A of polar relay I1 and conductor I9 to permitoperation over longer lines, without a detrimental decrease in thenormal current due to resistance in the printer contact.-

This short circuit also serves to prevent false starting of the printermotor before the call is completed. To make a call, calling key 2| isdepressed and released thus releasing cut-off relay II and operatingline relay 23 and causing the line finder I05 to connect the linethrough to a selecting circuit. As the line relay of the selectingcircuit and its battery tap resistor are of lower resistance than thewinding of the cutoiT relay II and its battery tap resistor, the linecurrent now increases. This increase may be observed in meter I03indicating that the calling station may dial. The off normal contactsI02 of the dial I are arranged to connect a local negative potentialfrom battery I01 to the line and prevent the printer motor M fromstarting in response to: the dial pulses. The dial of the subscribersstation may now be operated to actuate the switch of the selectingcircuit to select the class of service required. Assuming that thesubscriber called in order to send a telegram, the digit dialed will besuch that a group of secondary line finders associated with centralofiice operators printers will be selected. The first idle secondaryfinder I09 of this group will operate to extend the line through tooperator's printer set III. When the line is switched through to thecentral oflice printer, the line current reverses, polar relay IIreleases, thus removing the short circuit from the printer magnet 43,short circuiting control relay 39 through back contacts of the polarrelay, thus starting printer motor 4|. The circuit is now establishedfor the subscriber to transmit his message. After the desiredcommunication has been concluded the circuit is released in the samemanner as that described in connection with Fig. 1.

In the low current system as shown in Fig. 6, the line circuit normallyextends through both the high and low resistance windings 53 and 55respectively, of polar relay 5|, through a calling key designatedgenerally as H3 and through a back contact II5 of control relay 39 toground. The high resistance winding 53 limits the line current to a lowvalue, for example about six milliamperes, such that cut-ofi relay II(Fig. 4) releases and line relay 23 does not operate. Polar relay 5Iwill operate on this low current however. When the calling key isoperated it connects dial lamp II! and its shunt resistance across thehigh resistance winding 53 of polar relay 5| and removes the shortcircuit from the dial pulsing contacts by opening contacts H8. The linecurrent now increases from the normal value up to a higher value, forexample about forty milliamperes. The increased line current operatesline relay 23 (Fig. 4) and causes the circuit to be switched through theline finder I05 to the selecting circuit I 01 (Fig. 5). The line currentnow increases to a higher value, for example about sixty milliamperes,and the dial lamp III lights up indicating that the circuit is ready fordialing. The oif normal contacts II9 of the dial IOI open the windingsof control relay 39 to prevent starting of the motor even though polarrelay 5I responds to the pulses.

The dial at the subscribers station may now be operated to connect thesubscriber through the primary line finders and secondary line findersI05 and I09 to the operators printer set III. The subscriber maylikewise be connected through a tollboard jack or a repeater controlunit for local exchange service, as described in my Patent 1,895,113 orthe Hallden Patent 1,895,- 097. As this particular connection is notneeded for an understanding of my invention as disclosed herein,illustration thereof has not been made.

After connection has been established at the central oifice, positivepotential from the central ofiice is supplied to the line thus reversingthe line current causing polar relay 5| to operate to close contact I20energizing control relay 39 and starting the station printer motor 4|.The control relay also removes the short circuit from the keyboardcontacts and printing magnet 43 and establishes a short circuit aroundthe high resistance winding 53 of polar relay Hand the dial lamp IIT.Calling key II3 should now be restored to the normal central position.Release of this circuit is controlled from the central office in thesame manner as that described in connection with Fig. 3.

In the event the central station desires to be connected with aparticular subscribers line such connection is established by dialingfrom outward o'perators printer such as I2I through selector I23 andconnector circuit I25 to private and line bank contacts P1, L1, andthrough the line to the particular printer station, in the mannerdisclosed in my Patent No. 1,895,113.

If a local station-to-station call between two subscribers is desiredafter operating calling key II 3 and waiting for dial lamp II! to light,as described, one digit is dialed to select this class of service. Thisincreases the line resistance at the selecting circuit to extinguish thedial lamp until the line is connected through the secondary finder tothe repeater control unit at which time the dial lamp is again brightlylighted. Further operation of the dial controls selectors and connectorsto extend the circuit to the called station line after which the callingkey is restored to its normal center position. This reconnects the highresistance winding of the polar relay 5| into the line, reduces the linecurrent to normal value and causes the repeater control unit to connectthe calling and called station lines through a single line reepaterconnecting a positive potential to both lines.

This system is not illustrated herein but is fully set forth in theHallden Patent No. 1,895,097.

The positive potential thus applied causes polar relays 5! at both thecalled and the calling station to operate their respective controlrelays 39 starting the motors 4| and increasing the line current to itsnormal working value, in the same manner as set forth above in thedescription of the circuit of Fig. 6.

To release these connections the calling key at the subscribers stationmay be operated to its clear out position, to the left as shown in Fig.6. This opens the contact 121 removing the short from clear out relayI29 and allowing 'it to operate in series with control relay 39. Theclear out relay locks itself in operated position through contacts NHand establishes a short circuit around control relay 39 which thenreleases stopping motor 4| and reducing the line current again to thenormal non-operating value. This low current permits a slow actingrelay, not shown, associated with the single line repeater, not shown,to release the connection. Current from a negative battery on the linethen operates through polar relay 5| releasing the clear out relay andrestoring the circuit to normal.

The high current circuit, such as shown in Fig. 4, may be used insubstantially the same manner for local exchange service. For adaptingthis system to such service a resistance 20, of substantially the sameresistance value as high resistance 53 of polar relay M, is shuntedacross calling key 2|. After operating calling key 2| and receiving theusual indication in meter I03, one digit is dialed on dial IOI to selectthe local exchange service. Calling key 2| is then operated to reducethe line current by reinserting resistance 2| in circuit, causing therepeater control unit to connect the calling and called station linesthrough a single line repeater, connecting a positive potential to bothlines. When the positive potential is applied to line 3 current reversesin meter I93.- The subscriber then releases calling key 2'I and circuitis established in the manner described above.

Release of this connection may be accomplished by manipulation of key2|, to reduce the line current to a low value as described above. Thisdrop in current permits the slow acting relay associated with the singleline repeater to release, opening the line connection. The circuit atsubscribers station then returns to its normal unoperated condition in amanner similar to that described in connection with Fig. 1.

In an automatic concentration system of either of the types described,during periods of heavy traffic all of the printer sets at the centraloilice for receiving or sending telegrams and their associated automaticswitches may be busy, with the result that incoming calls or outgoingmessages may be delayed. Additional printer sets can be provided, but ifthese are connected in the usual way additional automatic switchingequipment must also be provided. This involves a considerable expensefor equipment that is only used for a comparatively short time each day.During such periods, certain subscribers stations will have enoughtraffic to keep a central office printer continually busy, or nearly so,and it is, therefore, desirable to table them or, in other words, toconnect them directly with certain central ofiice printer sets. need forrapid switching on such connections, as they are set up and leftconnected for fairly long periods of time. Arrangements are provided,therefore, for making these connections with cords and jacks to avoidthe expense of providing automatic switches. As there may be some idleperiods, even during busy hours, on such circuits it is desirable toequip them with calling and motor control arrangements.

To take care of such cases, a group of central oflice printer sets isprovided, each set being connected as shown in Fig. 7. Each linecircuit, as shown in Figs. 1 and 4, has a line jack 290 for use withcords such as 20! of the tabling printers. When it is desired to table aparticular line, a cord MI is plugged into the line jack 200. The extracontacts on the jack ground the P bank contacts, making this line testbusy to all outgoing calls, and operating both the line relay and thecut-off relay. The subscribers line 3 is now disconnected from itsregular line and cutoff relay and connected to relays II and 23associated with the tabling printer set shown in Fig. 7.

If the subscribers station is of the normal low current type, as shownin Fig. 3 or Fig. 6, relays H and 23 will remain released when the cordis plugged in. To call, the subscriber operates his calling key in theusual Way, thus increasing the line current and operating relay 23.Relay 28 looks itself through release key 203 and operates relay I I.The line is now connected through the B contacts of relays II and 23 tothe central office printer. Relay 23 also operates control relay 39 andlights the guard lamp 299 to call the central ofiice operators attentionto the call. The control relay connects positive battery to the centraloifice printer motor, starting it, and to the line, starting thesubscribers printer motor in the usual way. The subscriber may now sendhis message.

To release the connection, the operator depresses release key 203,releasing relay 23 which connects negative battery through its A contactand the winding of relay I I to the line. A guard There is no lamp isextinguished and the control relay'is released at this time. Thenegative battery on the line stops the subscribers printer motor in theusual way and cuts in the high resistance'winding of relay 5|, whichreleases relay 1 l, restoring the circuit to normal.

To call the station, the central oflice operator depresses call key 205to operate relays l I and 23, after which the circuit functions the sameas during an inward call. In the case of a high current line. relay llremains operated after the call is released, and the relays function inthe same manner as the usual line and cut-off relays for calling.

The remaining features of the system are substantially similar to thoseillustrated in Figs. 1 and 4 and need not be described in detail. Thecircuit connections of this printer may be readily followed by areference to the particular description made in connection with theother figures.

While the description given above refers generally to a'singesubscribers'station and its connection with the central ofiice, it is,of course, understood that in a system of automatic'printing telegraphy,such as described, any desired number of subscribers may be connected tothe central operators station in the usual manner.

While my invention has been described with particular reference to theattached drawings, such description is not intended as a limitationthereon. .My invention and the particular features for which I desireprotection are defined in the appended claims.

What I claim is:

1. In a printing telegraph system, a subsciibers station, a centralofiice, a line circuit from the subscribers station interconnecting saidstation and oflice, means at the central office for establishingconnection between the subscribers line circuit and an idle printer atsaid central ifice, and means operative alternatively in response to anincrease, or a decrease and a sub sequent increase in normal linecurrent for operating said first named means.

2. In a printing telegraph system, a plurality of subscribers stations,a line from each subscribers station to a central office, means at thecentral office for connecting said subscribers stations to an idleprinter, and means operative alternatively in response to a breaking ofsaid subscribers line circuit and subsequent closing of said line, or toincreased current on said line circuit for operating said connectingmeans.

3. A printing telegraph system as claimed in claim 1, further comprisinga release key and means operative upon manipulation of said release keyto restore said system to its original state.

4. In a printing telegraph system, a subscribers station, a subscribersprinter, a central oflice, a printer and a finder switch at said centraloffice, a line connecting said subscribers station to said centraloffice, means operative alternatively in response to an increase, or adecrease and subsequent increase of current in said line current tooperate a selecting means, means responsive to operation of saidselecting means to connect said line to said central printer, and meansresponsive to said last named connection, to operate said subscribersprinter.

5. In a telegraph concentrator circuit, a cutoff relay, a line relay,line windings on said relays connected with a source of current, otherwindings on said relays connected with a source of current and normallyin an open circuit, means responsive to a change in line current tochange the current through said line windings, and means responsive tosaid change in current to close the circuit through said other windingson both said relays.

6. In a line relay circuit, a line relay, a cut-off relay, windings onsaid relays, a line circuit'normally closing said cut-off relay windingand normally leaving said line relay winding open circuited, otherwindings on said cut-off and line relays, said last named relay windingsbeing mor mally open circuited, means responsive to opening and closingof said line circuit to open said normally closed relay winding andclose said normally open relay winding, and means responsive to theclosing of said normally open winding to close the circuit through saidother relay wind-l ings. v 7. In a line relay circuit as claimed inclaim 6, means for opening said second named relay. circuit, and meansresponsive to the opening of said circuit to restore the circuit tonormal.

8. In a linerelay circuit, a line relay, a cut-off relay, windings onsaid relays, a line circuit normally connected through said line relaywindings, the current in said line circuit being normally insufiicientto operate said relays, other windings,

normally open circuited, on said cut-off line relays, and meansresponsive to an increase of current in said line to close the circuitthrough said last named windings.

9. In a printing telegraph exchange system, a subscribers station,comprising a polar relay, a motor control relay and a calling key, aline connected to said subscribers station, a line relay circuit,comprising a slow release cut-ofi relay, a line relay and. a grouprelay, means operative upon operation of said calling key to cause saidline relay to operate said group relay, selective means operative uponenergization of said group relay to connect said relay circuit to acentral oflice printer, local windings on said cut-off and line relays,means responsive to said last named connection to energize said serieswindings, and means responsive to energization of said local windings toconnect said line to said central office printer and. to release saidmotor control relay.

10. In a printing telegraph system, a subscribers station, a centraloffice, a line from said subscribers station to said central oificestation, a printer set at said central office, a line control relaycircuit operative alternatively in response to an increase, or adecrease and a subsequent increase of normal current in said line forcontrolling the establishing of a circuit between said subscribersstation and said printer set, and means for connecting said printer setdirectly into said line.

11. In an exchange system, a station connected over a normally closedline with a central office, a source of line current at said centraloiiice, a cut-off relay at said central office normally energized bysaid line current, a normally deenergized line relay at said centraloffice, means at said station for momentarily decreasing said linecurrent to release said cut-off relay and to energize said line relay toinitiate a call at said central oflice, means responsive to said call toenergize both said relays and means responsive to the release of saidcall to release said line relay.

12. In an automatic printing telegraph exchange system, a plurality ofstations connected over single wire lines to a central office, relays ineach line at the central office for. controlling automatic switches,said relays being provided with means operative, alternatively byincreasing the line current above normal, or by first decreasing theline current below normal for operating said automatic switches and thenincreasing it to normal.

13. In a printing telegraph exchange system, a plurality of subscribersstations, a central office, a line from each subscribers station to saidcentral ofii-ce, printer sets at said central ofiice, means forconnecting anyone of said printer sets directly into any one of saidlines, and relay means in said printer set, operative alternatively inresponse to a decrease below normal and subsequent increase to normal orto an increase above normal of the line current to establishcommunication between said subscribers station and said central ofllce.

14. In an automatic exchange system, a plurality of subscribersstations, a central oiiice, line circuits from said subscribers stationsto said central ofiice, means at said central ofiice for communicatingwith said subscribers, a source of line current at said central oiiice,and means in each subscribers line operative alternatively in responseto. increase in line current, or a decrease and subsequent increase tonormal of said line current to establish connection between thesubscribers station and the central office communicating means.

15. In an automatic telegraph exchange system, a cut-off relay, a linerelay, line windings on said relays, a source of current for said linewindings, means responsive to a change in current in said line windingsto change the current through said windings, normally open circuitedlocal windings on said relays, and means responsive to said change incurrent in said line relays to close the circuit through said localwindings.

16. In an automatic exchange system, a station connected over a normallyclosed line with a central oflice, a source of current at said centraloffice,a line relay and a cut-ofi relay at said central station normallyin circuit with said source, means atsaid station for. increasing saidline current above normal, means responsive to said increase in linecurrent to open said cut-off relay circuit to initiate a call, and meansoperative in response to initiation of said call-to energize otherwindings on said relays.

GILBERT S. VERNAM.

